Cycloolefin resins are resins having a cyclic olefin skeleton in their backbone and having properties including high transparency, low birefringence, high heat deformation temperature, light weight, dimensional stability, low water-absorbency, hydrolysis resistance, chemical resistance, low-dielectric constant, low-dielectric loss, freedom from materials which present environmental problems. Consequently, cycloolefin resins are used in various fields which require the aforementioned properties.
Among them, in view of properties such as high heat resistance, high transparency, and low birefringence, cycloolefin resins are used as materials for transparent molding-processed articles in optical devices such as lenses, light guide plates, and diffraction gratings, and industrial materials used in the fields of construction, lighting, and the like.
When cycloolefin resins are used for optical elements, whether or not the resin elements can endure the usage environment becomes the most important factor. That is, it is required that optical properties do not deteriorate by resin deterioration due to the usage environment. Various conditions of the usage environment are envisioned depending on the article in question. However, especially tough environment conditions are assumed to be about 95° C. in temperature and about 95 RH in humidity. Therefore, it is required that the optical properties can be maintained without deterioration of the resins even when the resins are exposed to such environments.
However, a molded article made of cycloolefin resins becomes cloudy depending on its usage environment, and the transparency and light transmittance, which are properties of the resins, deteriorate. This fact adversely affects the usage of the resins in fields which requires transparency, such as optics applications. Particularly, environmental changes going to a normal humidity and normal temperature atmosphere after exposure to a high humidity and high temperature atmosphere posed the problem of clouding due to microcrack generation which occurs in a molded article made of cycloolefin resins, which intrinsically have low water-absorbency, when water vapor trapped in the article under the high temperature and high humidity atmosphere condenses inside the article without exiting therefrom under normal temperature and normal humidity.
For the purpose of preventing such a deterioration in the transparency of cycloolefin resins, resin compositions including cycloolefin resins together with an amine compound or amide compound, which have hydrophilic groups and hydrophobic groups in the same molecule, at a specific ratio have been proposed (Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Publication No. H09-176396